Combined hydrophobic-hydrophilic filter for fluids

ABSTRACT

A combined filter for removing an aqueous fluid and entities, such as bacteria, existing in such aqueous fluid, from a nonaqueous fluid. The combined filter consists of a hydrophilic filter and a hydrophobic filter that are arranged in fluid communication and serially to be placed along the flow path of a fluid. The hydrophilic filter and the hydrophobic filter may touch one another or be located some distance from one another. Also, a structure may be inserted into the space between the hydrophilic filter and the hydrophobic filter that will maintain the space between the hydrophilic filter and the hydrophobic filter without significantly restricting the flow of fluid. And, in one embodiment, the combined filter may be composed simply of material having both hydrophilic and hydrophobic characteristics on the molecular level. Preferably, however, the filters and spacing structure are contained within an encasement having an inlet and an outlet. As any filter or spacer is located farther downstream with respect to the intended flow of fluid, the dimensions of that filter or spacer in the direction perpendicular to the intended flow of fluid increase to a sufficient extent that, as the stream of fluid expands perpendicularly to its intended direction of flow, the possibility of the fluid contacting any solid element other than a filter is decreased.

BACKGROUND OF THE INVENTION

1. 1. Field of the Invention

2. This invention relates to a filter for removing an aqueous fluid andentities, such as bacteria, existing in such aqueous fluid, from anonaqueous fluid.

3. 2. Description of the Related Art

4. A number of patents are directed toward the combination of ahydrophobic filter and a hydrophilic filter for removing air or othergas from an intravenous fluid before such intravenous fluid reaches apatient. See, e.g., U.S. Pat. Nos. 4,013,072; 4,031,891; 4,116,646;4,262,668; 4,278,084; 4,515,606; 4,525,182; 4,571,244; 4,615,694;5,126,054; 5,308,333; 5,439,587; and 5,536,413.

5. None of the preceding patents, however, applies to a device whichfilters the fluid first through the hydrophobic filter and then throughthe hydrophilic filter or vice-versa. In each case, the intravenousliquid comes into contact with a hydrophobic filter through which gasfrom the liquid may escape and then the intravenous liquid passesthrough a hydrophilic filter.

6. Three patents do, though, apply to devices which transmit fluidthrough both a hydrophobic filter and a hydrophilic filter, viz., U.S.Pat. Nos. 4,026,792; 4,459,139; and 4,938,389.

7. U.S. Pat. No. 4,026,792 of George Otto Orth, Jr. applies to a “methodof treating waste water containing particulate matter, liquid oils andfats to remove the same . . . ” The disclosure indicates that this wastewater is first forced through a hydrophobic filter by centrifugal force.“Fats, oil and oily particulate matter are adsorbed by the hydrophobicfilter . . . . The remaining waste water then moves radially into thehydrophilic filter . . . which removes the remaining particulate matter.As indicated in column 3 of U.S. Pat. No. 4,459,139, “The keycharacteristic of the hydrophobic filter membrane is, of course, that itwill allow air or other gas to pass therethrough but will block thepassage of water or other aqueous liquids . . . [But] . . . ahydrophobic filter membrane has its own water-breakthrough point, i.e.,the amount of pressure differential across the membrane required todrive water through it.” For the method of U.S. Pat. No. 4,026,792 tofunction as intended, the centrifugal force must, therefore, besufficiently large that the pressure differential at least equals thewater-breakthrough point.

8. In U.S. Pat. No. 4,459,139 of Charles E. vonReis and Karlis Vizulis,itself, a device is claimed “having a hydrophilic filter in overlyingrelationship to [a] . . . hydrophobic filter on the inlet chamber sideof the hydrophobic filter such that any fluid flow from the inletchamber to the outlet chamber can only be by passage of the fluid firstthrough the hydrophilic filter and then through the hydrophobic filter .. . .” both the hydrophobic filter and the hydrophilic filter have apore size rating in air of less than 0.5 microns and, preferably, ofapproximately 0.2 microns; each then “ . . . blocks bacteria frompassing . . . .” These filters, furthermore, preclude liquid fromreaching a suction pump used to aspirate liquid from a patient. The factthat a significant pressure differential is created across the combinedfilters is evident from the following excerpts:

9. In columns 2 and 3, it is stated that “[i]n operation the aspiratorpulls a vacuum (i.e. a negative pressure) . . . to aspirate fluid fromthe patient . . . .”

10. The vonReis patent, in column 4, further observes, “The hydrophobicfilter used in the practice of the present invention should preferablyhave a water-breakthrough point of at least about 10 psi, and ideallyabove the maximum pressure differential which can be expected, i.e.about 14 psi for the aspirating system described.”

11. Columns 1 and 2 of the vonReis patent contain a declaration that,“[i]t is well known that a hydrophilic filter allows the passage of airtherethrough until it is saturated with liquid but blocks or at leastsubstantially restricts the passage of air when it does become saturatedwith liquid. Where the pressure differential across the hydrophilicfilter does not exceed the bubble point of the filter (i.e. the pressurerequired to force air through the filter when it is saturated withliquid), the passage of air is completely blocked when it becomessaturated. But even where the pressure differential does exceed thebubble point, the hydrophilic filter when saturated will neverthelesssubstantially restrict the passage of air.”

12. And, again in column 4 of the vonReis patent, one reads, “ . . . ina preferred embodiment the hydrophilic filter membrane used had a bubblepoint of from about 7 to 10 psi and as it reached saturation theblockage of air was about 80% . . . .”

13. U.S. Pat. No. 4,525,182 of Donald B. Rising and Richard G. Naegeli,Jr., in fact, asserts, “The typical small pore size of the wetted[hydrophilic] filter prevents gas from passing through said filter atthe usual operating pressures.” Moreover, using almost identicallanguage, U.S. Pat. No. 5,439,587 of Ralph J. Stankowski, Michael C.Heath, and Douglas A. Boucher asserts, “The typical small pore size ofthe hydrophilic filter prevents gas from passing through the filter atthe usual operating pressures.”

14. The third patent concerning a device which transmits fluid throughboth a hydrophobic filter and a hydrophilic filter, i.e., U.S. Pat. No.4,938,389 of Scott R. Rossi and Jeffrey P. Gilbard, claims a reservoirfor storing sterile liquids connected to a dispensing tip with a flowpassage across which a filter assembly is sealed. The filter assemblycomprises “a hydrophilic filter and a hydrophobic filter arranged influid communication serially along said flow passage so that saidhydrophilic filter is nearer to said reservoir than said hydrophobicfilter, said hydrophobic filter and said hydrophilic filter each havingpores sufficiently small to act as a microbial filters.”

15. “In preferred embodiments of the invention, the filter assembly hasthe hydrophobic and hydrophilic filters separated, e.g., by a supportring. A more preferred embodiment has a filter structure whereby thereare a plurality of support rings between, and on opposite sides of, thefilters to provide structural support and filter separation.”

16. Since the examples of the Rossi patent utilized an “eye dropsolution” as the sterile liquid, since solutions for rinsing a person'seyes are generally aqueous saline solutions, and since the Rossi patentwas not limited to nonaqueous solutions, it is apparent that asignificant pressure differential would have to be created across thehydrophobic filter, i.e., the water-breakthrough point would have to bereached, in order to permit the solution to pass through the hydrophobicfilter.

17. It should be noted that none of the preceding patents were intendedto remove water from another liquid.

18. Additionally, lines 11 through 12 in column 3 of U.S. Pat. No.5,126,054 clarify that the “[l]iquiphobic layer 18 is superimposed onliquiphilic layer 16 . . . .” Similarly, U.S. Pat. No. 5,536,413 impliesthat there is no space between the liquiphobic and the liquiphiliclayers of the gas venting element of that patent when it states that “.. . the layers of the gas venting element may be individually preparedand bonded together by various means known to those skilled in the art.”

19. Moreover, none of the filter material in the preceding patentscombines hydrophilic and hydrophobic characteristics on the molecularlevel. U.S. Pat. No. 4,031,891 of Thurman S. Jess does state, “While theinvention has been described above as using three different filterelements, namely a hydrophilic filter element to cover the centralwindow opening . . . and separate hydrophobic filter elements coveringthe opposing window openings . . . , it will be understood by thoseskilled in the art that use can also be made of a continuous sleeve offilter material, the ends of which have been rendered hydrophobic innature and the central portion of which has been rendered hydrophilic innature.” It is, however, apparent that the hydrophilic and thehydrophobic segments of the filter in the Jess patent are distinct fromone another on a macroscopic level. This is, also, true for the filtermaterial to which reference is made in U.S. Pat. No. 4,278,084 of J. LeePope, Jr.: “ . . . it has been suggested in U.S. Pat. No. 3,520,416 toKeedwell to use a microporous filter material which is hydrophilic insome areas, and hydrophobic, as by the application of siliconetreatment, in other areas.”

SUMMARY OF THE INVENTION

20. The present invention consists of a hydrophilic filter and ahydrophobic filter arranged in fluid communication serially along theflow path of a fluid.

21. In a first embodiment the pores of both the hydrophilic filter andof the hydrophobic filter are selected to be of such a size thatbacteria can not pass through either filter but that a gas such as aircan substantially freely traverse the filters.

22. In a second embodiment the pores can be larger since it is merelydesired to prevent an aqueous fluid, such as water, in a nonaqueousfluid, such as gasoline, from passing through the filters with thenonaqueous fluid.

23. In both embodiments, the hydrophilic filter and the hydrophobicfilter could touch one another, but it is preferred to maintain a spacebetween them to accommodate any of the fluid which is desired to beremoved that manages to pass the first filter in the flow path but notthe second filter. It is, furthermore, preferred to place within suchspace a structure that will maintain the space between the hydrophilicfilter and the hydrophobic filter without significantly restricting theflow of fluid. This facilitates drying of any fluid between thehydrophobic filter and the hydrophilic filter.

24. In fact, preferably an encasement having an inlet and an outletcontains the hydrophilic and the hydrophobic filters and possesses aspacer to maintain the hydrophobic filter physically separate from thehydrophilic filter. The hydrophilic filter is preferably placed so thatin use it will be upstream from the hydrophobic filter. As theencasement, filters, and spacer proceed in the direction that isintended to be downstream, the dimensions of the filters and spacerperpendicular to the intended direction of fluid flow increase so thatas the stream of fluid expands perpendicularly to its intended directionof flow, the possibility of the fluid contacting other than a filter andthereby precipitating some of any aqueous liquid that the fluid maycontain is decreased.

25. And an additional embodiment is composed of filter material whichhas both hydrophilic and hydrophobic characteristics on the molecularlevel.

BRIEF DESCRIPTION OF THE DRAWINGS

26.FIG. 1 illustrates the embodiment of the CombinedHydrophobic-Hydrophilic Filter for Fluids wherein the hydrophilic filtertouches the hydrophobic filter.

27.FIG. 2 portrays the embodiment which has a space between thehydrophilic filter and the hydrophobic filter.

28.FIG. 3 shows a honeycomb structure from above, which honeycombstructure is placed between the hydrophilic filter and the hydrophobicfilter to maintain a space between the hydrophilic filter and thehydrophobic filter without significantly restricting the flow of fluid.

29.FIG. 4 depicts the Combined Hydrophobic-Hydrophilic Filter for Fluidswherein a filter material is utilized which has both hydrophilic andhydrophobic characteristics on the molecular level.

30.FIG. 5 is a cutaway view from the side of the encasement containingthe hydrophobic filter, the hydrophilic filter, and the spacer.

31.FIG. 6 shows a view from either end of the encasement containing thehydrophobic filter, the hydrophilic filter, and the spacer.

DESCRIPTION OF THE PREFERRED EMBODIMENT

32. The Combined Hydrophobic-Hydrophilic Filter for Fluids, in a firstembodiment, comprises, as depicted in FIG. 1, a hydrophilic filter 1 anda hydrophobic filter 2 that are arranged in fluid communication andserially to be placed along the flow path of a fluid.

33. When the Combined Hydrophobic-Hydrophilic Filter for Fluids is to beutilized to remove an aqueous fluid, such as water, from a gas, such asair, the pores in both the hydrophilic filter 1 and the hydrophobicfilter 2 are preferably selected to be of such a size that bacteria cannot pass through either filter but that a gas, such as air, cansubstantially freely traverse both the hydrophilic filter 1 and thehydrophobic filter 2.

34. When, however, the Combined Hydrophobic-Hydrophilic Filter forFluids is to be used to prevent an aqueous fluid, such as water, in anonaqueous fluid, such as gasoline, from passing through the filterswith the nonaqueous fluid, the pores can be larger.

35. If one desires not only to preclude the passage of an aqueous fluid,but also to remove such aqueous fluid from a nonaqueous fluid, it ispreferable—as illustrated in FIG. 2—to have the hydrophilic filter 1located some distance from the hydrophobic filter 2 in order to create aspace 3 within which any on the aqueous fluid which manages to pass theupstream filter may collect. It is, moreover, preferable to have thehydrophilic filter 1 as the upstream filter because the aqueous fluidwill then either be absorbed into the hydrophilic filter 1 or pass intothe space 3 where it will remain because its further travel will beprecluded by the hydrophobic filter 2. When a significant quantity ofaqueous fluid collects within the space 3, either such aqueous fluid canbe removed from space 3 or the entire Combined Hydrophobic-HydrophilicFilter for Fluids can be removed from the flow path of a fluid andreplaced with another Combined Hydrophobic-Hydrophilic Filter forFluids.

36. In some circumstances it is desirable to maintain the space 3between the hydrophilic filter 1 and the hydrophobic filter 2 byinserting into the space 3 a structure that will maintain the spacebetween the hydrophilic filter and the hydrophobic filter withoutsignificantly restricting the flow of fluid, such as the honeycombmaterial depicted in FIG. 3.

37. In other circumstances it will be desirable to utilize as theCombined Hydrophobic-Hydrophilic Filter for Fluids material 4 havingboth hydrophilic and hydrophobic characteristics on the molecular level,as illustrated in FIG. 4.

38. A preferred structure for the Combined Hydrophobic-HydrophilicFilter for Fluids utilizes, as illustrated in FIG. 5, an encasement 5having an inlet 6 and an outlet 7. The encasement 5 contains one or morehydrophilic filters 1 and one or more hydrophobic filters 2. A spacer 8located between the hydrophilic filter or filters 1 and the hydrophobicfilters 2 maintains the space 3 by keeping the hydrophilic filters 1physically separate from the hydrophobic filters 2. As discussed above,the hydrophilic filter or filters 1 are preferably placed so that in usethe hydrophilic filter or filters 1 will be upstream from thehydrophobic filter or filters 2. And as the filters 1, 2 and spacer 8are located farther in the direction that is intended to be downstream,the dimensions of the filters 1, 2 and spacer 8 perpendicular to theintended direction of fluid flow increase to a sufficient extent that,as the stream of fluid 9 expands perpendicularly to its intendeddirection of flow, the possibility of the fluid contacting any solidelement other than a filter 1, 2 and thereby precipitating some of anyaqueous liquid that the fluid may contain, is decreased.

39. There are, of course, many applications for the CombinedHydrophobic-Hydrophilic Filter for Fluids. One is as a surgical mask orthe similar mask worn by those who must be in an environmentcontaminated with germs or dust. Another is as a device to removecontaminants from the air which is recirculated within an airplane.

40. An example of the Combined Hydrophobic-Hydrophilic Filter for Fluidsutilized to remove bacteria from air is:

EXAMPLE

41. Heat and Moisture Exchange Media (HME), which is commerciallyavailable from 3M Filtration Products of St. Paul, Minn., was used forthe hydrophilic filter; and Filtrete Air Filter Media Type S, which is,also, commercially available from 3M Filtration Products of St. Paul,Minn., was utilized for the hydrophobic filter.

42. Five filters were tested. The differential pressure across eachfilter, utilizing an air flow of 8 liters per minute, was 14.5 mm H₂Ofor Filter no. 1, 15.2 mm H₂O for Filter no. 2, 17.5 mm H₂O for Filterno. 3, 14.7 mm H₂O for Filter no. 4, and 15.5 mm H₂O for Filter no. 5.

43. A test procedure was conducted to determine the Bacterial FiltrationEfficiency (BFE), a ratio of (a) the difference between the number ofcolony forming units (CFU) in the challenge delivered to the filter andthe number of colony forming units in the sample tested after passagethrough the filter to (b) the number of colony forming units (CFU) inthe challenge delivered to the filter.${B\underset{\_}{F}E\%} = {\frac{C - T}{C} \times 100}$

44. where C is the average control value for the number of colonyforming units (CFU) in the challenge delivered to the filter, and T isthe number of colony forming units in the sample tested after passagethrough the filter.

45. A culture of Staphylococcus aureus was diluted in 1.5% peptone waterto a precise concentration to yield challenge level counts of 2200±500colony forming units per test sample. The bacterial culture suspensionwas pumped through a “Chicago” nebulizer at a controlled flow rate andfixed air pressure. The constant challenge delivery, at a fixed airpressure, formed aerosol droplets with a mean particle size ofapproximately 3.0 μm. The aerosol droplets were generated in a glassaerosol chamber and drawn through a six-stage, viable particle Andersensampler for collection. The sampler was maintained at 28.3 liters perminute (1 cubic foot per minute). Test controls and test samples werechallenged for a two-minute interval.

46. The delivery rate of the challenge also produced a consistentchallenge level of 2200±500 CFU on the test control plates. A testcontrol (which had no filter in the airstream) and reference materialwere included after 7 to 10 test samples. The Andersen sampler, a sievesampler, impinged the aerosol droplets onto six agar plates based on thesize of each droplet. The agar medium used was soybean casein digestagar (SCDA). The agar plates were incubated at 37° C.±2° C. for 48±3hours. The colonies formed by each bacteria-laden aerosol droplet werethen counted and convert to “probable-hit” values using the holeconversion chart provided by Andersen.

47. Each of the five filters achieved a BFE exceeding 99.9 percent. Infact, there were no detected colonies on any of the Andersen samplerplates for Filter no. 1, Filter no. 3, and Filter no.4.

48. It should, moreover, be noted that the test procedure utilizedproduces a more severe challenge to most filtration materials than wouldbe expected in normal use.

I claim:
 1. A combined hydrophobic-hydrophilic filter for fluids, whichcomprises: an encasement having an inlet and an outlet; one or morehydrophilic filters; one or more hydrophobic filters arranged in fluidcommunication and serially with said hydrophilic filters; and a spacerlocated between said hydrophilic filter or filters and said hydrophobicfilter or filters, wherein the dimensions of said filter or filters andsaid spacer perpendicular to the intended direction of fluid flowincrease the farther such filter or filters and said spacer are locateddownstream with respect to the intended direction of fluid flow to asufficient extent that, as the stream of fluid expands perpendicularlyto its intended direction of flow, the possibility of the fluidcontacting any solid element other than a filter is decreased.
 2. Thecombined hydrophobic-hydrophilic filter for fluids as recited in claim 1, wherein: the pores of both said one or more hydrophilic filters andsaid one or more hydrophobic filters are selected to be of such a sizethat bacteria can not pass through either the hydrophilic filter or thehydrophobic filter but that a gas can substantially freely traverse boththe hydrophilic filter or filters and the hydrophobic filter or filters.3. The combined hydrophobic-hydrophilic filter for fluids as recited inclaim 2 , wherein: said hydrophilic filter or filters are located sothat in use said hydrophilic filter or filters will be upstream withrespect to the intended direction of fluid flow from said hydrophilicfilter or filters.
 4. The combined hydrophobic-hydrophilic filter forfluids as recited in claim 1 , wherein: said hydrophilic filter orfilters are located so that in use said hydrophilic filter or filterswill be upstream with respect to the intended direction of fluid flowfrom said hydrophilic filter or filters.
 5. A process for removing anaqueous fluid from being combined with a nonaqueous fluid, whichcomprises: causing the combined fluids to enter the inlet of anencasement; causing the combined fluids to flow through one or morehydrophilic filters within such encasement, which one or morehydrophilic filters will absorb the aqueous fluid; causing the combinedfluids to encounter a hydrophobic filter, which hydrophobic filter willnot permit the aqueous fluid to pass but which will allow the nonaqueousfluid to flow through the hydrophobic filter; maintaining suchhydrophilic filter or filters physically apart from such hydrophobicfilter or filters; and having the dimensions of the hydrophilic filteror filters, the hydrophobic filter or filters, and the spacerperpendicular to the intended direction of fluid flow increase thefarther the hydrophilic filter or filters, the hydrophobic filter orfilters are located downstream with respect to the intended direction offluid flow to a sufficient extent that, as the stream of fluid expandsperpendicularly to its intended direction of flow, the possibility ofthe fluid contacting any solid element other than a filter is decreased.6. The process for removing an aqueous fluid from being combined with anonaqueous fluid as recited in claim 5 , further comprising: selectingthe pores of both the one or more hydrophilic filters and the one ormore hydrophobic filters to be of such a size that bacteria can not passthrough either the hydrophilic filter or the hydrophobic filter but thata gas can substantially freely traverse both the hydrophilic filter orfilters and the hydrophobic filter or filters.
 7. The process forremoving an aqueous fluid from being combined with a nonaqueous fluid asrecited in claim 6 , further comprising: locating the hydrophilic filteror filters so that in use the hydrophilic filter or filters will beupstream with respect to the intended direction of fluid flow from thehydrophilic filter or filters.
 8. The process for removing an aqueousfluid from being combined with a nonaqueous fluid as recited in claim 5, further comprising: locating the hydrophilic filter or filters so thatin use the hydrophilic filter or filters will be upstream with respectto the intended direction of fluid flow from the hydrophilic filter orfilters.